1. Field of the Invention
The present invention relates to a composite optic fibre for laser with pump and laser wave confinement, it enables the realisation of high power lasers and may be applied to the realisation of laser systems of diverse types. The term laser covers any application wherein the light-emitting capacity of the fibre by electronic de-energisation of elements having been placed beforehand in electronic energised state, is implemented, this concerning the lasers as well as, more generally, the optical amplifiers. The fibre of the invention although it may be used in continuous emission lasers, enables to obtain more particularly interesting results in pulse-operated lasers.
2. Description of the Related Art
The operating principle of the laser is known, it consists, generally speaking, in transferring a so-called pump energy to a material medium for placing into energised electronic state elements of this medium, thereby creating an inversion of population, elements which will retrieve a basic electronic state while emitting an electromagnetic radiation coherently and at a predetermined wavelength thanks to an amplifying structure promoting these emission characteristics.
However, the conversion of energy is not perfect in a laser. On the one hand, all the pump energy is not used by the medium for the inversion of population and the amplifier gain G is expressed as being proportional to the ratio between the pump fluence Jp (energy density or, in the case of continuous emission, intensity) and a parameter of the medium called saturation fluence Jsat: G=exp(Jp/Jsat) and when the material exhibits high saturation fluence, high pump fluence should be used. On the other hand, during the emission, the emission wavelength is different, smaller, from that having been used for pumping and a portion of the excitation energy of the medium is not converted in the emission radiation and generates heat in the medium. Thus, if the material has high Jsat, the gain then being low, the pump power density should be high and the heat generated may become such that it reaches the fracture threshold of the material. Finally, the material media are not perfect optically and may exhibit absorption effects, diffraction or others which are sometimes non linear in relation to the energies involve which compromise the quality of the radiation transmitted.
Thus, in power lasers, it is particularly difficult to combine the average power, the energy and the spatial quality. Current high power lasers enable either to generate high powers and high pulse-operated energies, with detriment to the spatial quality of the beam, case of slab lasers or, still, thin disk lasers, or high powers, but without any possibility of pulse-operated radiation with small pulse width, case of fibre lasers.